Various metals in UV-B

[otoien]

"The UV protection filter being transparent in UVB is quite hilarious."

 

We often call them UV-protective filters, but for instance  the Nikon NC-filters do not claim to filter out any UV. One has to go to L37 or L39 for that. NC-filters have coatings though that one would expect to at least cause some attenuation of UV.

[lukaszgryglicki]

I know this for a rather long time, I never use them for UV filtering, I use them as a lens protectors.

 

[ulf]

6 hours ago, otoien said:

NC-filters have coatings though that one would expect to at least cause some attenuation of UV.

They do, but not enough to be significant, because it is just two surfaces.

Further down into UV the effect increases and designs for deeper UV normally cannot have AR-coating, at least not if the wavelength range is wide.

A modern lens with many coated surfaces get more attenuation, beside from the effect of some used glass types.

 

I did some experiments coating a cheap "UV-Protector glass" and saw some improvement of the transmission, especially closer to 300nm:

https://www.ultravioletphotography.com/content/index.php?/topic/4043-rain-x-changes-a-filters-transmission/

The gain of transmission is not worth the trouble compared to the transition losses of around 5% per surface, but the coating might improve the resistance of humidity corrosion of some filter materials.

 

[lukaszgryglicki]

I will be doing similar experiment with many filters when I have some time. Will see how they "look like" in 300nm - 320nm range.

 

[ulf]

43 minutes ago, lukaszgryglicki said:

I will be doing similar experiment with many filters when I have some time. Will see how they "look like" in 300nm - 320nm range.

 

If you reach the same improvement of around 1%, as I measured, I do not think you will be able to see any difference at all.

 

Lately I have tried to improve the dirt rejection of my Zomei 850nm IR-filter with Rain-X.

First I polished the surface really clean with Cerium oxide for a virgin surface for the Rain-X reaction.

As the filter is blackish changes in reflection is clearly visible.

The treated surface gets more dark, but it is difficult to get an even treatment.

One of the sides looks terrible as some areas got less deep treatment.

 

I will try to redo the experiment in a more controlled way, separately protecting the opposite side, not under treatment.

It takes some time to polish off the treated surface completely to start over.

After polishing in the end the surface reflexion is clearly brighter. 

 

[lukaszgryglicki]

I mean I only wanted to photograph them (various filtersd in UV-B), nothing else.

[colinbm]

@lukaszgryglicki Where could I get a polished Silicon Sphere please ?

[lukaszgryglicki]

kranite.com: https://www.kickstarter.com/projects/trancemetals/one-kilogram-silicon-sphere-trance-metals

 

[colinbm]

10 minutes ago, lukaszgryglicki said:

kranite.com: https://www.kickstarter.com/projects/trancemetals/one-kilogram-silicon-sphere-trance-metals

 

Did yours cost $1000 ?

 

 

[lukaszgryglicki]

Something like this, I don't remember, it was some time ago.

 

I've found an email from 3 years ago:

 

[colinbm]

OK thank you.

[Stefano]

That silicon sphere will become transparent at about 1100 nm, at the border between NIR and SWIR. I'm not sure you can see it with a normal camera.

[lukaszgryglicki]

I don't think it will.

Germanium is transparent in 7-14um - I saw this many times with my FLIR thermal camera, but silicon is not transparent around 1 um... is it?

I tried to "see" this once - but it is still opaque for my cameras - I only have either normal 0.3um -> 1.1um (full spectrum) or thermal (7-14 um).

[Stefano]

It looks like many metals would be colored in multispectral photos: https://www.researchgate.net/figure/Spectral-reflectivity-of-perfectly-smooth-metal-surfaces-3_fig1_236582531

[dabateman]

1 hour ago, Stefano said:

It looks like many metals would be colored in multispectral photos: https://www.researchgate.net/figure/Spectral-reflectivity-of-perfectly-smooth-metal-surfaces-3_fig1_236582531

Well most of the excitement is below 300nm or even less than 200nm.

Only one that jumps out is nickel, and you might have just caught its UVB dip, or near its darkest point.

[lukaszgryglicki]

I don't have any good filtering option below 300nm :(

 

[Stefano]

I was thinking about TriColour either in the "sun UV" range (300-400 nm) or something like UV-VIS-IR. I think copper and gold wouldn't be the only colored metals.

[photoni]

@lukaszgryglickiwonderful collection of metals.

I photographed jewels and metals for 20 years (the most difficult are steel pots)
I believe that to have visible differences between metals they should all be: flat, opaque (acid satin), and photographed with a sun veiled by a cloud

the spherical shape and hard light are misleading

[Stefano]

For TriColour, I would get one of these reflectance standards: https://www.google.com/url?sa=t&source=web&rct=j&url=https://sphereoptics.de/en/product/zenith-polymer-reflectance-standards/&ved=2ahUKEwicwqXM4p__AhVvQ_EDHePIC40QFnoECBkQAQ&usg=AOvVaw0-xuUe7MDrafcBJli4IoUD

 

https://www.google.com/url?sa=t&source=web&rct=j&url=https://sphereoptics.de/en/wp-content/uploads/sites/3/2014/03/SphereOptics-Diffuse-Reflectance-Standards-Targets-Materials-Zenith-Polymer.pdf&ved=2ahUKEwicwqXM4p__AhVvQ_EDHePIC40QFnoECBgQAQ&usg=AOvVaw3jktJ-yvFIZI1csSNr1wvl

 

I would get the 25% one. The standard must not be overexposed to be useful, so if the subject is dark (as often happens in UV), the standard must not be too bright. These are rated for the 250-2450 nm range.